Such a device is known. It was disclosed in the work entitled “Der Chronometer Gang” by Professor Alois Irk and published by Deutsche Uhrmacher Zeitung, Berlin 1923. Reference will be made particularly to paragraphs 116 to 120 (pages 74 to 77) and to FIG. 25 of the cited work.
This device is implemented in so called detent escapements which are suitable for timepieces of large dimensions such as marine chronometers. These timepieces are appreciated for their high level of precision, which is why they very often use a detent escapement, which itself famed for its high level of precision. This escapement has, however, a significant drawback, namely its sensitivity to shocks. Consequently, it is reputed to be unsuitable for wristwatches. In fact, a shock applied to the timepiece can cause its balance to rotate beyond a normal operating angle. This then produces tripping since unlocking and pulses occur twice in the same vibration.
When one wishes to fit a timepiece of small dimensions, for example a wristwatch, with a detent escapement to replace for example the conventional lever escapement and thus enable it to enjoy the advantages provided by such an escapement, new techniques will have to be used, different to those known to date if one wishes to avoid failure. Various solutions have been proposed recently to overcome the lack of energy developed by the sprung balance of a wristwatch to overcome the forces acting on the detent of a detent escapement. Nonetheless, the problem of tripping remains, and this has to be resolved when a balance spring of small dimensions, such as that mounted in a wristwatch, is used.
If one refers to the aforecited work, it can be seen that the locking arm proposed for the anti-trip device is suitable solely for a balance spring of large dimensions. It is in fact a part that has undergone machining several times including the machining of a bore through which the last coil of the balance spring will pass. This is ill suited to a balance spring of small dimensions, moreover it is difficult and complicated to make.
In order to overcome the aforecited drawbacks, the present invention, in addition to answering the generic definition of the first paragraph of this description, is characterized in that the locking arm is a clamp hooked onto the outer coil of the balance spring.